The current formal criteria for diagnosing Alzheimer's require steadily progressing memory loss and an inability to carry out day-to-day activities, like dressing or bathing - along with a pathologist's report of plaque and another abnormality, known as tangles, in the brain after death.

Nor do scientists fully understand what causes it, though for years, opposing camps have duked it out over hypotheses that have focused largely on brain abnormalities called tangles, neither of which has so far proved a good therapeutic target.

As the snowy sash creaked in my hand, he made off to the waterspout that suspends its "tangles" of ice over a gaping tank, and, rebounding from that, with a quiver of his little black breast, bobbed through the network of wire and joined a few of his fellows in a forlorn hop round the henhouse in search of food.